Why? Could it not also be interpreted as the ultimate sign of his attraction for you? That his attraction is so strong that his body responds even while he is unconscious?
Ok sure, if this had happened a time or two, and he was fun and sexy about it even while fully asleep, I'd love it!
But my experience with people who act things out while they are fully asleep hasn't been very good. People can kick, punch, shove and grab you so hard they can leave bruises. They cannot respond to you, they do not know you exist, you are not "you", you are some dream image to them, and they have super human strength. It can be very frightening. If they speak to you, they are not speaking to "you". And they do not act in rational ways, because they are dreaming, so even what could be a nice grope, if he's totally asleep, it can quickly turn into a shove or a punch or a squeeze so hard you leap out of bed. Because he wouldn't know what he was doing nor be able to gauge your reaction in the least. You can't mess around with someone who has super human strength and absolutely no sense of reality.
I require enough consciousness being present to understand consent.
But as I said...if I had experienced my boyfriend in a fully asleep state just sexily touching and groping me, sure, that would be fun.
I had one experience with an ex, where we both apparently slipped into a sex dream about each other and both went for each other at the same time in our sleep! We woke up having sex! We were both stunned! It was really fun because it was so odd and different, and it was like what you said about our bodies just going at each other without us even having to be involved...so it felt really primal and sexual. That did not happen exactly like that ever again, but there were a few times when he said I started climbing on top of him in my sleep, he didn't discourage me and was willing to participate, but he said once I got up there I just passed out on top of him all dead weight. Not too sexy by then, ha! And there were a couple of times he did something of the same thing to me...came after me with a night erection seemingly just awake and initiating sex, but when I started responding and trying to kiss him he was essentially dead weight again.
He actually also grabbed my wrist once while he was dreaming about something random and he almost broke it.
He had no idea. It was scary. That only happened once, thank god.